1. Field of the Invention
This invention relates in general to a dynamic bearing device (a fluid dynamic bearing device) for supporting a rotational member in a non-contact manner by a dynamic action of lubrication oil generated in a bearing gap. The bearing device is suitable for a spindle motor of an information machine, for example, a magnetic disk device such as HDD, FDD, an optical disk device such as CD-ROM, CD-R/RW, DVD-ROM/RAM, and a magnetic optical disc device such as MD, MO; a polygon scanner motor of a laser beam printer (LBP); or a small-size motor of an axial flow fan, etc. in an electronic equipment.
2. Description of Related Art
For various motors mentioned above, in addition to high rotational accuracy, high speed, low cost and low noise etc., are requested. One of the constructional elements that define these requested performances is a bearing that supports a spindle of the motor. Recently, for such a kind of the bearing, a dynamic bearing superior in the above requested performances has been considered to be used, or has been implemented in practice.
For example, a dynamic bearing device, which is installed in a spindle motor of a disk device such as HDD, comprises a radial bearing portion for rotatably supporting an axis member in a non-contact manner in the radial direction, and a thrust bearing portion for rotatably supporting the axis member in a non-contact manner in the thrust direction.
For each of these bearing portions, a dynamic bearing that has dynamic pressure generating grooves formed on a bearing surface thereof is used. The dynamic pressure generating grooves of the radial bearing portion are formed on an inner circumferential surface of a bearing sleeve or an outer circumferential surface of the axis member. The dynamic pressure generating grooves of the thrust bearing portion, when using an axis member with a flange portion, are formed on both end faces of the flange portion, or on surfaces opposite thereto (for example, on an end face of the bearing sleeve, an end face of a thrust member disposed on a bottom portion of a housing and the like), respectively. Conventionally, the bearing sleeve is fixed to a predetermined position on an inner circumference of the housing. Additionally, when the bottom portion of the housing is formed with the thrust member, a step portion for positioning the thrust member is often formed on the housing (the positioning of the thrust member with respect to the housing is performed by fitting the thrust member to the step portion). Furthermore, in order to prevent the lubrication oil that is filled into the internal space of the housing from externally leaking, a sealing member is often disposed at an opening portion of the housing.
The aforementioned dynamic bearing device comprises parts such as the housing, the bearing sleeve, the axis member, the thrust member and the sealing member. In order to secure high bearing property required as the information equipment getting more and more high performances, efforts for improving accuracy of each part and accuracy of assembling have been made. In particular, the dimension of the thrust bearing gap is affected by accuracy of parts, such as the axial dimension of the flange portion of the axis member, the surface accuracy of the both end faces of the flange portion, the surface accuracy of the end faces of the bearing sleeve and the thrust member that form thrust bearing surfaces, and by accuracy of assembling, such as the axial space between the bearing sleeve and the thrust member, so that it is very difficult to control the dimension of the thrust bearing gap to be within the desired value. As a result, in the actual situation, it is forced to perform processes of parts with higher accuracy or more complicate assembling than necessary. Meanwhile, accompanying the low cost trend for the information equipment, a request to the dynamic bearing device for lowering cost becomes to be more and more severe.